1. Technical Field
Bioactive phenolic extracts applicable in the food, dietary, cosmetic and pharmaceutical industry.
2. Relevant-Background
Proanthocyanidinins or condensed tannins are oligomers and polymers of flavan-3-ol widely distributed in the plant kingdom. The most abundant units of flavan-3-ol are (+)-afzelechin, (+)-catechin and (+)-gallocatechin (forms 2R:3S) and their diasteroisomer (−)-epiafzelechin, (−)-epicatechin and (−)-epigallocatechin (forms 2R:3R), respectively. Proanthocyanidinins exclusively constituted by (epi)catechin are called procyanidins. Propelargonidins and prodelphinidins contain at least one unit of (epi)afzelechin and (epi)gallocatechin, respectively, together with units of (epi)catechin. In the B-type procyanidins/propelargonidins/prodelphinidins, the units of flavan-3-ol are bound by the C-4 carbon of the upper unit and the C-6 or C-8 carbon of the lower unit, C4-C8 isomers being more abundant than C4-C6. In addition to this interflavonic C—C bond, the A-type procyanidins have a bond of ether-type between the C-2 carbon of the upper unit and the hydroxyl group of the C-7 of the lower unit (Porter L. J. (1988) Flavans and proanthocyanidins. In The flavonoids (Harborne J. B., Ed.) Chapman and Hall, New York, pp. 21-62). Whilst B-type proanthocyanidinins are found in many plant species, there a few natural sources where A-type proanthocyanidinins have been identified (bilberry, peanut, avocado, plum, cinnamon and curry); likewise, procyanidins are the majority with respect to propelargonidins and prodelphinidins in the plant kingdom (Prior R. L., Gu L. (2005) Occurrence and biological significance of proanthocyanidin in the American diet. Phytochemistry 66, 2264-2280).
  Flavan-3-olR1R2C-2C-3(+)-AfzelechinHHRS(+)-CatechinHOHRS(+)-GallocatechinOHOHRS(−)-EpiafzelechinHHRR(−)-EpicatechinHOHRR(−)-EpigallocatechinOHOHRR
Products rich in proanthocyanidinins most widely marketed at present are currently obtained from sources such grape seeds, apple, cocoa, pine bark, etc., and mainly contain B-type procyanidins. A-type proanthocyanidinins have properties/activities that are potentially beneficial for human health, such as reduction of the capacity of bacterial adhesion in the urinary tract—which reduces the risk of urinary infections (Foo L. Y., Lu Y. R., Howell A. B., Vorsa N. (2000) A-type proanthocyanidin trimers from cranberry that inhibit adherence of uropathogenic P-fimbriated Escherichia coli. J Nat. Prod. 63, 1225-1228; Foo L. Y., Lu Y. R., Howell A. B., Vorsa N. (2000) The structure of cranberry proanthocyanidins which inhibit adherence of uropathogenic P-fimbriated Escherichia coli in vitro. Phytochemistry 54, 173-181), and the pseudoinsulin activity, which improves glucose metabolism in patients with type 2 diabetes—(Anderson R. A., Broadhurst C. L., Polansky M. M., Schmidt W. F., Khan A., Flanagan V. P., Shoene N. W., Graves D. J. (2004) Isolation and characterization of polyphenol A-type polymers from cinnamon with insulin-like biological activity. J. Agric. Food Chem. 52, 65-70). Antioxidant activities have also been demonstrated (Barreiros A. L. B. S., David J. P., de Queiroz L. P., David J. M. (2000) A-type proanthocyanidin antioxidant from Dioclea lasiophylla. Phytochemistry 55, 805-808) as have anti-inflammatory activity (Lin L. C., Kuo Y. C., Chou C. J. (2002) Immunomodulatory proanthocyanidins from Ecdysanthera utilis. J. Nat. Prod. 65, 505-508) for A-type proanthocyanidinins.
Having stated the above, the interest therefore arises for new products rich in the three types of proanthocyanidinins—i.e., procyanidins, propelargonidins, and prodelphinidins—especially with A-type bonds. Some earlier publications related to products containing proanthocyanidinins are the following:
WO2005/072726: Compositions and methods of use of A-type procyanidins, Schmitz, H. H.; Kwik-Uribe, C. L.; Kelm, M. A.; Hammerstone, J. F. This publication relates to formulations to be used in treatment for hypertension. A-type procyanidins are exclusively included, in other words, formed exclusively by (epi)catechin.
WO2004/112813: Litchi sinensis extracts containing oligomeric proanthocyanidins, Rull, S.; Alaoui, I.; Fabry, B. This publication relates to the preparation of litchi extracts rich in A-type proanthocyanidinins, although identifications of the type of molecules contained in the extract are not included.
US2004/156925: Plant proanthocyanidin extract effective at inhibiting utility, Howell, A. B.; Vorsa, N. This publication relates to the preparation of extracts of proanthocyanidinins for the prevention and treatment of infections of the urinary tract caused by Escherichia coli type P. The extracts contain proanthocyanidinins with at least one A-type bond, particularly procyanidins.
WO99/12541: Plant proanthocyanidin extract effective at inhibiting adherence of bacteria with P-type fimbriae to surfaces, Howell, A. B.; Vorsa, N. This publication relates to the preparation of extracts of proanthocyanidinins from the Ericaceae, Rosaceae, Pinaceae and Vitaceae families, preferably Vaccinium macrocarpon. The extracts are used in the prevention and treatment of urinary tract infections caused by P-type Escherichia coli. 
US2002/028260: Proanthocyanidin composition extracted from Vaccinium useful in pharmaceutical compositions for preventing or treating urogenital infection, Mickelsen, J. N.; Mickelsen, R. A.; Walker, E. B. This publication relates to the use of certain procyanidins (A and B) against urinary infections and others. Although the title speaks of proanthocyanidinins, in the text it indicates that they are formed by (epi)catechin units, (i.e. procyanidins).
US2002/0228260: Plant proanthocyanidin extracts, Walter, E. B.; Mickelsen, R. A.; Mickelsen, J. N. This publication relates to plant extracts containing procyanidins with at least one A-type bond and their use in the prevention and treatment of urogenital infections.
ES2171142: Flavanol and cysteamine conjugates. Torres, J. L. It relates to new products which result from the conjugation of polyphenolic extracts rich in procyanidins and prodelphinidins with molecules which contain the thiol group.
An important point in development of products rich in potentially active compounds is their cost, both of initial raw material and preparation method. In this sense, food industry by-products are attractive sources of bioactive compounds.
The tegument or skin of the almond, which is separated from the almond during the industrial processing thereof, is a by-product with little economic value, mainly used as cattle fodder. Various phenolic compounds have been identified in almond skin, both of non-flavanoid type and flavanoid type (Sang, S.; Lapsley, K.; Jeong, W-S.; Lachance, P. A.; Ho, C-T; Rosen, R. T. (2002) Antioxidant phenolic compounds isolated from almond skins (Prunus amygdalus Batsch). J. Agric. Food Chem., 50, 2459-2463; Milbury P. E., Chen C. A N D., Dolnikowski G. G., Blumberg J. B. (2006) Determination of flavonoids and phenolics and their distribution in almonds. J Agric Food Chem 54 , 5027-5033; Wijeratne S S K, Abou-Zaid M M, Shahidi F. (2006) Antioxidants polyphenols in almond and its coproducts. J Agric Food Chem, 54, 312-318). In relation to flavan-3-ols, Brieskon, C. H.; Betz, R. (1998) Procyanidin polymers crucial to the structure of the almond seed coat. Z. Lebensm. Unters. Forsch. 187, 347-353, identified the monomers (+)-catechin and (−)-epicatechin, as well as the dimmers of procyanidins B1, B3 and B4. Later, Lazarus, S. A., Adamson, G. E., Hammerstone, J. F., Schmitz, H. H. (1999) High performance liquid chromatography/mass spectrometry analysis of proanthocyanidins in food and beverages. J. Agric. Food Chem. 47, 3693-3701, confirms the presence of B-type procyanidins, also demonstrating the absence of A-type procyanidins in the extracts obtained from almond skin.